An automatic gearbox for a vehicle is typically controlled by a gearbox ECU (Electronic Control Unit), which controls gear selection so as to achieve an engine operation considered appropriate. A set of parameters and indicators may be considered when determining an initiation of a gear change. Such a set typically comprises the vehicle speed and an indication of whether a TCS (Traction Control System) is activated or not. The TCS typically comprises wheel-speed sensors and an ABS (Antilock braking system)/TCS-ECU. The ABS/TCS-ECU inter alia controls the wheel brake for a driven wheel which shows a tendency to spin and/or adapts the engine torque to a drive torque which can be transferred to the road, so that the vehicle retains its stability.
Especially when driving uphill on a smooth or slippery road or when cornering, the driven wheels may spin. The TCS is therefore activated and a message is sent to the gearbox ECU from the ABS/TCS-ECU that the TCS is activated. If the gearbox ECU detects that the TCS is activated, a gear change, such as an undesired upshift when driving uphill, is prevented in order to not cause inconvenience for the driver as well as disturbing queues of other vehicles behind the vehicle. This is especially true if the vehicle is heavy, such as a truck or a bus, which generally has a longer acceleration time than an ordinary car. U.S. Pat. No. 6,490,516-B1 discloses a method wherein an electronic gear control receives signals from a TCS.
Unfortunately, sometimes an undesired gear change is initiated anyway although one of the driven wheels has started to spin. The reason for this may be that the TCS is slow and the message informing that the TCS is activated arrives too late to the gearbox ECU.